.postage-calculator-box {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 25px;
border: 1px solid #e1e4e8;
border-radius: 12px;
background-color: #ffffff;
box-shadow: 0 4px 15px rgba(0,0,0,0.05);
}
.postage-calculator-box h2 {
color: #003366;
text-align: center;
margin-top: 0;
font-size: 24px;
}
.calc-row {
margin-bottom: 20px;
}
.calc-row label {
display: block;
font-weight: 600;
margin-bottom: 8px;
color: #333;
}
.calc-row select, .calc-row input {
width: 100%;
padding: 12px;
border: 1px solid #ccc;
border-radius: 6px;
box-sizing: border-box;
font-size: 16px;
}
.calc-btn {
width: 100%;
padding: 15px;
background-color: #003366;
color: white;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background 0.3s;
}
.calc-btn:hover {
background-color: #002244;
}
#postageResult {
margin-top: 25px;
padding: 20px;
background-color: #f0f7ff;
border-left: 5px solid #003366;
border-radius: 4px;
display: none;
}
.result-title {
font-weight: bold;
color: #003366;
font-size: 18px;
margin-bottom: 5px;
}
.result-value {
font-size: 28px;
font-weight: 800;
color: #222;
}
.postage-content {
line-height: 1.6;
color: #444;
margin-top: 40px;
}
.postage-content h3 {
color: #003366;
border-bottom: 2px solid #eee;
padding-bottom: 10px;
}
.postage-content table {
width: 100%;
border-collapse: collapse;
margin: 20px 0;
}
.postage-content th, .postage-content td {
padding: 12px;
border: 1px solid #ddd;
text-align: left;
}
.postage-content th {
background-color: #f8f9fa;
}
US Postage Rates Calculator (2024)
Type of Mail
Standard Letter (First-Class)
Postcard
Large Envelope (Flat)
Weight (Ounces)
Calculate Postage Cost
How US Postage Rates are Calculated
Calculating postage for United States Postal Service (USPS) mail depends primarily on three factors: the shape of the mailpiece, the weight, and the service class. As of the most recent rate adjustment in July 2024, the USPS has updated the prices for Forever Stamps and commercial mail.
Standard Letters: These are typical envelopes. The "Forever Stamp" covers the first ounce. If your letter exceeds 3.5 ounces, it is automatically reclassified as a Large Envelope (Flat) and charged a higher rate.
Postcards: To qualify for postcard rates, the card must be rectangular and meet specific dimension requirements (at least 3.5″ x 5″ but no larger than 4.25″ x 6″).
Large Envelopes (Flats): These are larger than standard letters (exceeding 6.125″ x 11.5″ or 1/4″ thickness) but must remain flexible. They are capped at 13 ounces; anything heavier must be sent via Priority Mail.
2024 USPS Postage Rate Table
Mail Type
First Ounce (Base)
Addl. Ounce
First-Class Letter
$0.73
$0.28
Postcard
$0.56
N/A
Large Envelope (Flat)
$1.50
$0.28
Examples of Postage Math
2-Ounce Letter: $0.73 (1st oz) + $0.28 (2nd oz) = $1.01 3-Ounce Large Envelope: $1.50 (1st oz) + $0.56 (2 extra oz) = $2.06 Standard Postcard: Flat rate of $0.56 regardless of destination within the US.
function calculatePostage() {
var mailType = document.getElementById("mailType").value;
var weight = parseFloat(document.getElementById("mailWeight").value);
var finalPrice = 0;
var note = "";
var resultDiv = document.getElementById("postageResult");
var priceDisplay = document.getElementById("finalPrice");
var noteDisplay = document.getElementById("postageNote");
if (isNaN(weight) || weight 3.5) {
// Letters over 3.5 oz are charged as flats
var roundedWeight = Math.ceil(weight);
if (roundedWeight > 13) {
finalPrice = "Priority Rates Apply";
note = "Letters over 13 oz must be shipped via Priority Mail.";
} else {
finalPrice = "$" + (flatBase + (roundedWeight – 1) * additionalOunce).toFixed(2);
note = "Note: Since the weight exceeds 3.5 oz, this letter is priced at Large Envelope (Flat) rates.";
}
} else {
var roundedWeight = Math.ceil(weight);
finalPrice = "$" + (letterBase + (roundedWeight – 1) * additionalOunce).toFixed(2);
note = "Standard First-Class Mail rate applied.";
}
} else if (mailType === "postcard") {
finalPrice = "$" + postcardBase.toFixed(2);
note = "Postcards have a flat rate regardless of weight (up to limits).";
} else if (mailType === "flat") {
var roundedWeight = Math.ceil(weight);
if (roundedWeight > 13) {
finalPrice = "Priority Rates Apply";
note = "Large envelopes over 13 oz must be shipped via Priority Mail.";
} else {
finalPrice = "$" + (flatBase + (roundedWeight – 1) * additionalOunce).toFixed(2);
note = "First-Class Large Envelope (Flat) rate applied.";
}
}
priceDisplay.innerHTML = finalPrice;
noteDisplay.innerHTML = note;
resultDiv.style.display = "block";
}